Let see:
That mast was not a stealth concept, the AEM/S concept was created in order to house and protect radar antennas. The radar housed in that mast was the same original systems that the ship carried, an SPS-40 air search radar, and the TACTASS Mk.23 low flying target finder.
The AEM/S mast was built fiberglass material.
Regards
Tomcat_I